For decentralized power generation, so-called gensets are often used, which are internal combustion engines coupled to a generator (usually a synchronous generator). For this application, common internal combustion engines can achieve powers of up to 10 MW (megawatts) or even higher and have corresponding dimensions.
In operation, these internal combustion engines run at a predetermined speed of the mains frequency, for example 1000 revolutions per minute at 50 Hz mains frequency and with a number of pole pairs of 3.
Usually, the excitation power of the synchronous machine required at the rotor is transmitted to the rotor via a brushless auxiliary machine.
For the general background, reference is made, for example, to DE2235058 (A1), which shows an arrangement for the excitation of an asynchronously starting synchronous machine.
To overcome the heavy starting torques, starting such internal combustion engines requires high-power starters. For internal combustion engines over 5 MW, as a rule pneumatic starters, mostly electric starters, are used. In particular, pneumatic starters are very expensive and require a lot of space.
Therefore, both for the excitement of the synchronous generator and for starting the internal combustion engine, expensive additional equipment is required.